The invention relates to integrated circuits, and in particular to circuits having a guard ring for protecting a sensitive part of the integrated circuit from another part of the integrated circuit, which could have a detrimental effect on the sensitive area. More specifically, the invention relates to a high voltage (HV) guard ring for protecting a sensitive low voltage area from a high voltage area on the same integrated circuit.
When integrated circuits operate at high voltages they can induce high energy particles that drift over the surface of the integrated circuit. These particles can adversely affect certain types of circuitry, in particular low voltage CMOS circuits, which are on the same integrated circuit.
A conventional method of shielding sensitive circuitry is to place metal or silicon guard rings around the sensitive areas. However, this method does not always prevent the drift of high energy particles over the surface of the silicon because the guard rings are beneath the top layer of isolating passivation.
The aim of the present invention is to provide an improved method of shielding high energy particles, thereby preventing them from disturbing sensitive circuitry.
According to the present invention, there is provided a guard ring for shielding a first area of an integrated circuit from a second area of the integrated circuit, the integrated circuit having at least an oxide isolation layer, a semiconductor layer and a passivation layer, wherein the guard ring comprises: a conductive guard ring which is partially exposed through the passivation layer in the integrated circuit; a semiconductor guard ring which is isolated from the remaining semiconductor in the semiconductor layer by at least two trench rings, one located on each side of the semiconductor guard ring; and, a plurality of conductive elements for electrically connecting the conductive guard ring and the semiconductor guard ring at spaced apart intervals, the conductive guard ring, semiconductor guard ring and conductive elements all being connected to a ground source.
According a further aspect of the invention, there is provided an integrated circuit having a guard ring for protecting a first area the integrated circuit from a second area thereof, the integrated circuit having at least an oxide isolation layer, a semiconductor layer and a passivation layer, wherein the guard ring comprises: a conductive guard ring which is partially exposed through a passivation layer in the integrated circuit; a semiconductor guard ring which is isolated from the remaining semiconductor in the semiconductor layer by at least two trench rings, one located on each side of the semiconductor guard ring; and, a plurality of conductive elements for electrically connecting the conductive guard ring and the semiconductor guard ring at spaced intervals, the conductive guard ring, semiconductor guard ring and conductive elements all being connected to a ground source.
According to yet a further aspect of the invention, there is provided a method of protecting a first area of an integrated circuit from a second area of the integrated circuit, in which the integrated circuit comprises at least an oxide isolation layer, a semiconductor layer and passivation layer, the method comprising the steps of providing a guard ring around the first area of the integrated circuit, wherein the guard ring comprises: a semiconductor guard ring for isolating the semiconductor layer in the first area of the integrated circuit from the remaining semiconductor in the second area of the integrated circuit; and, a conductive guard ring for attracting any harmful effects emanating from the second area, and conducting them to the ground.